The
red giant phase of a smallstar like the Sun will eventuallychange. The star loses some of its
gas into space and thecore contracts, gets brighter again
and becomes a white dwarf.

A
white dwarf, as the name suggests, is
verysmall (for a star).
The mass has contracted so much
that it has become very dense,
perhaps one million times
as
dense as any material on
Earth.
A
white dwarf does not have nuclear reactions but can be very hot.

What is a Black Dwarf?

In time a white
dwarf loses energy, cools down, stops shining
and becomes a black
dwarf.
A black dwarf can no longer
be seen because it is not emitting any
light. It may become
part of what is called "dark matter". It is not
known how
much dark
matter there is in the universe. Some astronomersbelieve that a
very large amount of dark matter
may exist.